The present invention relates to a digital driving method and apparatus for active matrix organic light emitting diode (AMOLED) and particularly a digital driving method and pixel structures that achieve the program-display-separated driving scheme by controlling the electric potential of the supply line.
The known TFT technologies at present can be classified in amorphous silicon TFT (a-Si TFT) and Poly-Si TFT. The generally called TFT-LCD is a-Si TFT which is technically well developed and is the main stream of LCD products. The main difference between the low temperature Poly-Si TFT (LTPS TFT) and the a-Si TFT is that the LTPS transistor requires a laser annealing during the manufacturing process to transform the thin film of amorphous silicon to poly silicon thin film so that the silicon structure of the LTPS is more organized than a-Si TFT. It can increase electron mobility up to 200 cm2/V-sec. The LTPS technology enables elements to be made in a smaller size. The size of the whole TFT element can be shrunk 50% or more. The aperture ratio may also be improved. Comparing with a-Si TFF of the same dimension, LTPS TFT has a higher resolution and lower power consumption. On design consideration, the driver module or a portion of Driver IC may be directly integrated on the glass substrate. This helps to reduce the size and element number required on the circuit board, and reduce the connection between the driver IC and the electrodes of the panel. As a result, circuit cost decreases. In addition, during packaging processes in the later stage of production, product damage may be reduced, and production yield increases, and production cost is lower. Moreover, as a portion of the driver IC is integrated, IC weight is reduced. Materials required in the assembly at the later production stage is less, and total weight may be greatly reduced. Furthermore, LTPS TFT has other advantages such as power saving, greater light intensity, finer picture, thin and light, fewer connection points (less than 200 connection points, that improves yields, while a-Si TFT has more than 3842 connection points).
However, during the manufacturing process of LTPS the properties of thin film transistor will change. When the driver system uses analog modulation method to display gray scale, the TFT often results in different properties after laser annealing process. Hence even if signals of the same voltage are programmed, the OLEDs of different pixels generate different current and produce different light intensity. This phenomenon tends to make the OLED panel to display erroneous gray scale images and severely damage image uniformity.
Therefore the primary object of the invention is to resolve the aforesaid disadvantages. The invention provides a digital driving method and pixel structures that achieve the program-display-separated driving scheme by controlling the electric potential of the supply line. During the image data program period, the electric potential of the supply line 7 is held at zero potential (GND) to disable the OLED 4 from lighting. When to display the image data, the supply line is connected to a positive electric potential to allow the OLED to light.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.